1. Technical Field
The present invention relates to an image reading apparatus such as a scanner which reads an image of a document.
2. Related Art
In the related art, in an image reading apparatus, a sheet feeding type in which a transport unit which can transport a document sheet by sheet along a transport path is provided, and a document which is being transported is read by a reading unit which is disposed at a predetermined position in the middle of the transport path, and a flat-bed type in which a carriage moves relatively to a document which is mounted on a document stand, and a reading unit provided in the carriage reads the document have been known.
Meanwhile, in the image reading apparatus of the sheet feeding type, there are a needs for reading an image of a booklet document which is formed of a plurality of pages such as a passport, or a bank book, or an image of a folded document such as a resume. The transport unit is provided with a separating mechanism which separates the plurality of documents which are mounted on a document support sheet by sheet.
There is a case in which it is not possible to appropriately read an image of a booklet document such as a passport, or a folded document such as a resume, since the image is shifted aslant, or the like, due to a force which is applied so as to separate the document sheet by sheet from the separating mechanism, when the document is transported. For this reason, there is a case in which an image of the booklet document or the folded document is read, by interposing the document of the booklet document or the folded document between a colorless-transparent carrier sheet which is formed by bonding one end portion of two sheets, and transporting the carrier sheet.
For example, in JP-A-2013-63843, a document reading apparatus which is provided with an ultrasonic sensor (double feeding detecting unit) which detects double feeding in which a plurality of documents are transported by being overlapped has been disclosed. The ultrasonic sensor includes an ultrasonic transmitter and an ultrasonic receiver which are disposed by facing each other, by interposing a transport path of a medium therebetween. In addition, a type detecting unit which classifies a first medium, and a second medium which is thicker than the first medium which are transported on the transport path, and a double feeding detecting unit which detects whether or not there is double feeding of a medium which is transported, based on an output of the ultrasonic sensor, and a detection result of the type detecting unit are provided in the document reading apparatus. An output intensity of the ultrasonic sensor is adjusted according to a paper thickness of a document which is being transported, and is detected by the type detecting unit. For example, when a transported document is a card document, an output intensity of the ultrasonic sensor is adjusted so as to be strong, compared to a paper document. For this reason, it is possible to prevent a card document from being erroneously detected as double feeding of a paper document.
Meanwhile, the carrier sheet is transported with a side of a bonding portion which is formed by bonding end portions of sheet portions of two pieces which interpose a document at the head. When the carrier sheet is transported, an ultrasonic wave from the transmitter of the double feeding detecting unit attenuates in an attenuation degree which is larger than that in the sheet portions of two pieces, compared to the bonding portion. For this reason, the carrier sheet is erroneously detected as double feeding of a paper document, and an image reading operation of a document is stopped. In order to avoid such an unintended stop of a reading operation, it is necessary to set up a countermeasure for providing an exclusive sensor for the carrier sheet in which it is possible to detect the carrier sheet by classifying thereof from double feeding of a document. In the technology which is described in JP-A-2013-63843, it is possible to adjust an output intensity of the ultrasonic sensor according to a paper thickness of a document; however, since an attenuation degree of an ultrasonic wave between the sheet portion of the carrier sheet and a doubly-fed portion of a paper document is relatively close to each other, there is a case in which it is not easy to discriminate both portions from each other, even when the output intensity of the ultrasonic sensor is adjusted, in addition to the fact that it is necessary to provide a type detecting unit which detects a paper thickness of a document.